Hydraulic valve

ABSTRACT

A stepped down groove  53  is provided around the peripheral surface of a rod portion  43  of a spool  40  which faces a third oil groove  33 . Both the axial ends  53   a  and  53   b  of the stepped down groove  53  are located axially outside of both the axial ends  33   a  and  33   b  of the third oil groove  33  at least while the valve is in pressure-adjusting condition. Also, another stepped down groove  52  is provided around a land  42  which faces a first oil groove  31 . Both the axial ends  52   a  and  52   b  of the stepped down groove  52  come, respectively, to the right and left sides of the axial end  31   b  of the first oil groove  31  to which end the spool  40  shifts to increase the opening of the oil groove at least while the valve is in pressure-adjusting condition.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a hydraulic valve whichcomprises a valve body, in which a spool-receiving room is provided toreceive a spool being inserted therein.

BACKGROUND OF THE INVENTION

[0002] A typical slide-type hydraulic valve comprises a valve body and aspool, which is accommodated and movable axially in a cylindricalspool-receiving room (also referred to as “bore”) provided in the valvebody. The valve body is provided additionally with a plurality of oilgrooves, which are formed perpendicularly to the central axis of thespool-receiving room, and with oil passages, which are providedextending from these oil grooves, to allow passage of hydraulic fluid oroil through the valve. Furthermore, the spool comprises lands, whichfunction as seals against flow of oil, and passages, which function aspassageways for flow of oil. In this construction of the hydraulicvalve, the spool is shifted axially in the spool-receiving room tochange the positions of the lands and passages of the spool with respectto the oil grooves of the valve body, so that an intended result can beachieved, for example, a change in the pressure or a change in the rateof oil flow through an oil passage. For shifting the position of thespool, the spool is connected to a lever, which can be manuallyoperated, or it is equipped with an appropriate device so that thehydraulic valve is operated hydraulically or electromagnetically inconsideration of the condition where the hydraulic valve is to beapplied.

[0003]FIG. 9 shows a regulator valve 100 as an example of such hydraulicvalve. The valve body 110 of the regulator valve 100 includes acylindrical spool-receiving room 111. The central part of thespool-receiving room 111 is connected to a first oil groove 121, whichlead to a main oil passage (not shown), where oil pressurized by ahydraulic pump (not shown) and adjusted by the regulator valve 100 isdelivered. On the left side of the first oil groove 121, a second oilgroove 122 is provided to connect to a lubrication oil passage (notshown). In this arrangement; although the spool 130 is biased leftwardby a spring 132 provided on the right side of the valve, if the pressureof the main oil passage is fed back through a third oil groove 123,which is provided on the left side of the valve, the spool 130 can shiftrightward overcoming the biasing force of the spring 132. Moreover, afourth oil groove 124 is provided on the right side of thespool-receiving room 111. When a control pressure is supplied into thefourth oil groove 124, this pressure generates a leftward biasing forceon the spool 130 additionally to that of the spring 132. In addition, afifth oil groove 125 provided on the left side of the third oil groove123 is connected to a drain oil passage.

[0004] A land 131, which is provided at the central portion of the spool130, is positioned in the first oil groove 121. When the leftwardbiasing force by the spring 132, the rightward biasing force generatedby the pressure supplied in the third oil groove 123, and the rightwardbiasing force generated by the pressure supplied in the fourth oilgroove 124 to set the regulator valve pressure, all these forces actingon the spool 130, are in equilibrium, the first oil groove 121 is influid communication with the second oil groove 122. In this condition,part of the oil being discharged from the hydraulic pump is led to thelubrication oil passage to maintain the pressure of the main oil passageat a constant pressure (line pressure).

[0005] By the way, the valve body 110 of the regulator valve 100 is anarticle of cast metal produced by die casting, so each of the first oilgroove 121, second oil groove 122, third oil groove 123 and fourth oilgroove 124 has a draft or slight taper, which is used for facilitatingthe removal of the die assembly during the production. Because of thepresence of a draft, the length of each oil groove in the direction ofthe axis of the spool 130 is smaller for the part of the oil groovelocated deeper in the valve body (part located lower in the drawing ofFIG. 9) and larger for the part located shallower. Therefore, the forceacting around the spool 130 (for example, the force acting on theperipheral surface of the land 131 in a direction perpendicular to theaxis of the spool 130) is stronger when the hydraulic pressure isreceived at a position shallower in each of the oil grooves. As aresult, an unbalanced load is generated in a direction from theshallower part to the deeper part of the valve body over the peripheralsurface of the spool 130, and this unbalanced load not only disturbs thesmooth movement of the spool 130 (hydraulic lock) but also erodes thevalve body 110. Furthermore, the unbalanced load can cause amisalignment of the spool 130 in the spool-receiving room 111, and thismisalignment, in turn, increases the amount of oil leak.

[0006] For alleviating the adverse effects of the unbalanced load actingon the spool, one method is to provide a labyrinth groove on theperipheral surface of the spool. However, forming such a labyrinthgroove requires a number of man-hours, and this method no way eliminatesthe unbalanced load itself. Therefore, the effectiveness of this methodis limited. Another method is to grind the inner surfaces of the oilgrooves to remove the drafts or slight tapers, which are created duringthe molding of the oil grooves. However, this method also requires anumber of man-hours and increases the production cost substantially.

[0007] On this background, it is an object of the present invention toprovide a hydraulic valve that maintains the smooth movement of thespool with little erosion of the valve body. This hydraulic valve shouldeliminate possibility of an unbalanced load to act on the spool, with alow cost, not requiring provision of a labyrinth groove or grinding ofthe inner surfaces of oil grooves.

DISCLOSURE OF THE INVENTION

[0008] To achieve the above objective, a hydraulic valve as a firstembodiment according to the present invention comprises a valve body anda spool, the valve body having a cylindrical spool-receiving room and anoil groove (for example, the third oil groove 33 described in thefollowing embodiment) provided orthogonally to the axis of thespool-receiving room. The spool is inserted in the spool-receiving room,so that the spool is shifted axially in correspondence to an actuationpressure supplied into the oil groove. In this hydraulic valve, astepped down groove is provided around the peripheral surface of thespool which faces the oil groove (for example, the peripheral surface ofthe rod portion 43 of the spool 40 described in the followingembodiment), such that both the axial ends of the stepped down grooveare located, respectively, axially outside of both the axial ends of theoil groove at least while the hydraulic valve is in pressure-adjustingcondition.

[0009] In this hydraulic valve, because a stepped down groove isprovided around the peripheral surface of the spool which faces the oilgroove, oil in the oil groove flows into the stepped down groove andpushes the peripheral surface in the direction perpendicular to the axisof the spool. Furthermore, because both the axial ends of the steppeddown groove are located axially outside of both the axial ends of theoil groove at least while the hydraulic valve is in pressure-adjustingcondition, the pushing force acting on the peripheral surface of thestepped down groove is distributed evenly all around the peripheralsurface. Therefore, no unbalanced force is generated around theperipheral surface, so the movement of the spool is smoother than thatof prior-art counterpart. In this favorable condition, no or littleunbalanced load acts to push the spool onto the valve body, so the valvebody is less prone to erosion than a prior-art counterpart.

[0010] A hydraulic valve as a second embodiment according to the presentinvention comprises a valve body and a spool, the valve body having acylindrical spool-receiving room and an oil groove (for example, thefirst oil groove 31 described in the following embodiment) providedorthogonally to the axis of the spool-receiving room. The spool isinserted in the spool-receiving room, so that the spool is shiftedaxially to change the axial length of the part of a land (for example,the land 42 described in the following embodiment) facing the oil grooveso as to adjust the opening of the oil groove. In this hydraulic valve,a stepped down groove is provided around the peripheral surface of theland so that both the axial ends of the stepped down groove come axiallyto the right and left sides, respectively, of the axial end of the oilgroove toward which end the spool shifts to increase the opening atleast while the valve is in pressure-adjusting condition.

[0011] In this hydraulic valve, because a stepped down groove isprovided around the peripheral surface of the land of the spool facingthe oil groove, oil in the oil groove flows into the stepped down grooveand pushes the peripheral surface in the direction perpendicular to theaxis of the spool. In this instance, because both the axial ends of thestepped down groove come axially to the right and left sides,respectively, of the axial end of the oil groove to which end the spoolshifts to increase the opening of the oil groove at least while thevalve is in pressure-adjusting condition, the pushing force acting onthe peripheral surface of the stepped down groove is distributed evenlyall around the peripheral surface. Therefore, no unbalanced force isgenerated to act around the peripheral surface, so the movement of thespool is smoother than that of a prior-art counterpart. In addition, thevalve body is less prone to erosion than a prior-art counterpart becauseno or little unbalanced load acts to push the spool onto the valve body.

[0012] A hydraulic valve as a third embodiment according to the presentinvention comprises a valve body and a spool, the valve body having acylindrical spool-receiving room and an oil groove provided orthogonallyto the axis of the spool-receiving room. The spool is inserted in thespool-receiving room, so that the spool is shifted axially to switchpositions so as to set the oil groove into fluid communication and intoblockage in correspondence to the respective switched positions. In thishydraulic valve, a stepped down groove is provided around the peripheralsurface of a land of the spool, so that the stepped down groove facesthe oil groove when the spool is positioned at each switched position.Furthermore, an axial end of the stepped down groove is located axiallyoutside of the oil groove notwithstanding the switched position of thespool.

[0013] In this hydraulic valve, because a stepped down groove isprovided around the peripheral surface of the land of the spool facingthe oil groove when the spool is positioned at each switched position,oil in the oil groove flows into the stepped down groove and pushes theperipheral surface in the direction perpendicular to the axis of thespool. In this instance, because an axial end of the stepped down groovecomes axially outside of the oil groove when the spool is at anyswitched position, the pushing force acting on the peripheral surface ofthe stepped down groove is distributed evenly all around the peripheralsurface. Therefore, no unbalanced force is generated around theperipheral surface, so the movement of the spool is smoother than thatof a prior-art counterpart. In addition, the valve body is less prone toerosion than a prior-art counterpart because no or little unbalancedload acts to push the spool onto the valve body.

[0014] Further scope of applicability of the present invention willbecome apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only and thus are not limitativeof the present invention.

[0016]FIG. 1 shows, along with adjacent oil passages, a hydraulic valveaccording to the present invention as first and second embodiments beingapplied as a regulator valve used for a vehicular transmission.

[0017]FIGS. 2A and 2B are enlarged views of the regulator valve shown inFIG. 1, FIG. 2A showing the condition of the valve where the spool isshifted a little rightward from its leftmost position, and FIG. 2Bshowing the condition where the spool is shifted further rightward.

[0018]FIG. 3 is a sectional view taken along line III-III in FIG. 2A.

[0019]FIG. 4 is an enlarged view of area IV in FIG. 2B.

[0020]FIG. 5 is an enlarged view of area V in FIG. 2B.

[0021]FIG. 6 shows a third embodiment of hydraulic valve according tothe present invention applied as a directional control valve, the spoolof the valve being positioned at a neutral position.

[0022]FIG. 7 shows this directional control valve, whose spool ispositioned at a rightward switched position.

[0023]FIG. 8 shows the directional control valve, whose spool ispositioned at a leftward switched position.

[0024]FIG. 9 shows a prior-art hydraulic valve.

THE BEST-MODE EMBODIMENTS OF THE INVENTION

[0025] Now, preferred embodiments according to the present invention aredescribed in reference to the drawings. FIG. 1 shows, along withadjacent oil passages, a hydraulic valve according to the presentinvention as first and second embodiments applied as a regulator valvefor a transmission used in a vehicle. FIGS. 2A and 2B are enlarged viewsof the regulator valve. FIG. 2A shows the condition of the regulatorvalve where the spool to be described below in detail is shifted alittle rightward from its leftmost position, and FIG. 2B shows thecondition where the spool is shifted further rightward from thecondition shown in FIG. 2A. While FIG. 3 is a sectional view taken alongline III-III in FIG. 2A, FIG. 4 is an enlarged view of area IV in FIG.2B, and FIG. 5 is an enlarged view of area V in FIG. 2B.

[0026] The regulator valve 10 comprises a valve body 20 and a spool 40,the valve body 20 having a spool-receiving room 21 whose inner surfaceis cylindrical, and the spool 40 being inserted and placed in thespool-receiving room 21. The spool-receiving room 21 comprises a firstreceiving room 21 a and a second receiving room 21 b, the firstreceiving room 21 a having an inner diameter larger than that of thesecond receiving room 21 b, which is located on the left side of thefirst receiving room 21 a. The valve body 20 is also provided with fiveoil grooves 31, 32, 33, 34 and 35, which are formed perpendicular to theaxis of the spool-receiving room 21 (the shape of the oil groove isshown in FIG. 3). The first oil groove 31 is located at the central partof the spool-receiving room 21 and connected to a pump oil passage L1,to which pressure oil is fed from a hydraulic pump (not shown), and to amain oil passage L2, to which the pressure oil adjusted by thisregulator valve 10 is discharged.

[0027] The second oil groove 32 is located on the left side of the firstoil groove 31 and connected to a lubrication oil passage L3, which isconnected to a lubricating oil supply circuit (not shown). The third oilgroove 33 is located at the right end of the second receiving room 21 band connected to a feedback oil passage L4 branched from the main oilpassage L2. The fourth oil groove 34 is located at the right side partof the first receiving room 21 a and connected to a regulator-pressuresetting pressure supply oil passage L5, which leads to aregulator-pressure setting circuit (not shown). The fifth oil groove 35is located at the left end of the spool-receiving room 21 and connectedto a drain oil passage L6, which leads to an oil tank (not shown), inthis embodiment. Depending on a requirement, this oil groove may beconnected to another oil passage.

[0028] The spool 40 comprises centrally located right and left lands 42and 41, whose diameter is relatively large, and between these lands 41and 42, a passage 44 is provided as a connection passage for hydraulicoil. These lands 41 and 42 and the passage 44 are positioned in thefirst receiving room 21 a. In this condition, part of the right-sideland 42 is located in the first oil groove 31 while part of the passage44 is located in the second oil groove 32. The spool 40 furthercomprises a rod portion 43 which is provided on the left side of theleft-side land 41 and whose outer diameter is smaller than that of thelands 41 and 42. The rod portion 43 is located in the second receivingroom 21 b (also partially in the third oil groove 33). The spool 40includes a spring-mounting room 47 at the right end, where a spring S isplaced in compressed condition to always bias the spool 40 leftward.

[0029] As shown in FIGS. 2A and 2B and FIG. 4, the spool 40 is providedwith a stepped down groove 53 around the rod portion 43 facing the thirdoil groove 33. The width of the stepped down groove 53 is constant inthe axial direction and is so wide that the axial ends 53 a and 53 b ofthe stepped down groove 53 are located axially outside of the axial ends33 a and 33 b of the third oil groove 33 at least while the regulatorvalve is set in pressure-adjusting condition (i.e., while the spool 40is at a position in the spool-receiving room 21 where it is returned alittle from the full stroke or leftmost end). As shown in FIGS. 2A and2B and FIG. 5, the spool 40 is provided also with a stepped down groove52 around the land 42 facing the first oil groove 31. The stepped downgroove 52 is so positioned on the spool 40 that the axial ends 52 a and52 b of the stepped down groove 52 having a constant width axially come,respectively, to the right and left sides of the axial end 31 b of thefirst oil groove 31 (in this example) when the spool 40 shifts(rightward in this example) to increase the opening of the valve body 20at least while the regulator valve is in pressure-adjusting condition.These stepped down grooves 52 and 53 are to eliminate the possibility ofunbalanced loads that may otherwise act on the spool 40, unbalancedloads being generated because of the existence of drafts on the oilgrooves 31 and 33 from the molding process (this function of the steppeddown grooves is described in detail, later).

[0030] The third oil groove 33, which is connected to the feedback oilpassage L4 branched from the main oil passage L2 as described above,receives the pressure oil from the main oil passage L2. Therefore, thespool 40 receives a rightward force that is generated by the pressure ofthe oil in the main oil passage L2, which pressure is supplied in thethird oil groove 33. When this rightward force increases correspondinglyto the increase of the pressure being received in the third oil groove33, the spool 40 shifts rightward overcoming the leftward biasing forceof the spring S and the leftward biasing force generated by theregulator-pressure setting pressure being supplied in the fourth oilgroove 34 from the regulator-pressure setting pressure supply oilpassage L5.

[0031] While the hydraulic pump is not operated, the first oil groove 31does not receive pressure oil, so the main oil passage L2 does notreceive pressure oil, either. In this condition, as the third oil groove33 as well as the fourth oil groove 34 does not receive pressure oil,the spool 40 receiving only the leftward biasing force of the spring Sis maintained stationary with the left end of the rod portion 43 beingin contact to the left end inner wall of the fifth oil groove 35 (referto FIG. 1).

[0032] When the operation of the hydraulic pump is started, the pressureoil from the hydraulic pump is supplied directly into the first oilgroove 31 and then to the main oil passage L2. Immediately after thepressure oil has entered the main oil passage L2, it is led through thefeedback oil passage L4 into the third oil groove 33. As a result, thespool 40 is shifted rightward connecting the first oil groove 31 and thesecond oil groove 32 through the passage 44 of the spool 40. In thiscondition, part of the oil in the pump oil passage L1 is led to thelubrication oil passage L3. The resultant condition now reduces thepressure of the main oil passage L2 and weakens the rightward biasingforce acting on the spool 40, so the spool 40 is now shifted leftward.As the spool 40 shifts leftward, more part of the land 42 is positionedin the first oil groove 31, reducing the opening of the first oil groove31. As a result, the flow of oil escaping to the lubrication oil passageL3 is reduced to increase the pressure of the main oil passage L2. Asthe pressure of the main oil passage L2 increases, the pressure of thethird oil groove 33 also increases to shift the spool 40 rightward. Asthe spool 40 shifts rightward, less part of the land 42 is positioned inthe first oil groove 31, increasing the opening of the first oil groove31. Now, the flow of oil escaping to the lubrication oil passage L3increases again, reducing the pressure of the main oil passage L2.

[0033] In this way, the regulator valve 10 is operated to control thepressure of the main oil passage L2 by the axial movement of the spool40, which changes the axial length of the part of the land 42 staying inthe first oil groove 31, thereby adjusting the opening of the first oilgroove 31. While the spool 40 repeats axial movements as describedabove, it takes a position where an equilibrium is achieved among theleftward biasing force of the spring S, the rightward biasing force bythe pressure oil supplied in the third oil groove 33, and the leftwardbiasing force by the pressure oil supplied in the fourth oil groove 34.As a result, the pressure of the main oil passage L2 or line pressure ismaintained at constant. However, the regulator-pressure setting pressurebeing supplied into the fourth oil groove 34 through theregulator-pressure setting pressure supply oil passage L5 is set to avalue higher than a normal value when the vehicle needs a large torque.When the regulator-pressure setting pressure at a higher value issupplied into the fourth oil groove 34, the pressure necessary for thespool 40 to shift rightward overcoming this increased pressure of thefourth oil groove 34, i.e., the pressure of the main oil passage L2, isincreased to achieve a new equilibrium. In this way, the line pressureis increased.

[0034] By the way, the valve body 20 of the regulator valve 10 is anarticle of cast metal produced by die casting, so each of the abovementioned oil grooves 31, 32, 33, 34 and 35 and other oil grooves has adraft or slight taper, which is used for facilitating the removal of thedie assembly during the production of the valve body. Because of theexistence of a draft, the length of each oil groove in the axialdirection of the spool 40 is smaller for the part of the oil groovelocated deeper in the valve body (part located lower in the drawing) andlarger for the part located shallower. In the regulator valve 10, asdescribed above, the rod portion 43 of the spool 40 facing the third oilgroove 33 is provided with a stepped down, groove 53, which extendsaround the peripheral surface of the rod portion 43. Therefore, the oilin the third oil groove 33 flows into the stepped down groove 53 andsurrounds and pushes the peripheral surface in the directionperpendicular to the axis of the spool 40 (in the upward and downwarddirections in the drawing). Because the axial ends 53 a and 53 b of thestepped down groove 53 are located axially outside of the axial ends 33a and 33 b of the third oil groove 33 at least while the regulator valveis in pressure-adjusting condition as described above, the pushing forceacting on the peripheral surface of the stepped down groove 53 isdistributed evenly all around the peripheral surface. Therefore, nounbalanced force is generated around the peripheral surface, so themovement of the spool 40 is smoother than that of a prior-artcounterpart. In addition, the valve body 20 is less prone to erosionthan a prior-art counterpart because no or little unbalanced load actsto push the spool 40 onto the valve body 20.

[0035] Also, as described above, the land 42 of the spool 40 facing thefirst oil groove 31 is provided with a stepped down groove 52, whichextends around the peripheral surface of the land 42. Therefore, the oilin the first oil groove 31 flows into the stepped down groove 52 andsurrounds and pushes the peripheral surface in the directionperpendicular to the axis of the spool 40 (in the upward and downwarddirections in the drawing). Because the axial ends 52 a and 52 b of thestepped down groove 52 come, respectively, to the right and left sidesof the axial end 31 b of the first oil groove 31 to which end the spool40 shifts to increase the opening of the oil groove at least while theregulator valve is in pressure-adjusting condition as described above,the pushing force acting on the peripheral surface of the stepped downgroove is distributed evenly all around the peripheral surface.Therefore, no unbalanced force is generated around the peripheralsurface, so the movement of the spool 40 is smoother than that of aprior-art counterpart. Accordingly, the valve body 20 is less prone toerosion than a prior-art counterpart because no or little unbalancedload acts to push the spool 40 onto the valve body 20.

[0036] In the above description, each of the stepped down grooves 52 and53 is described to have a constant width in the axial direction.However, it is not necessary for each stepped down groove to have aconstant width all around the spool 40. The same beneficial effect canbe achieved by forming the stepped down grooves in an up-and-downsymmetry in the cross-section of the spool 40. In this way, the areas ofthe stepped down grooves 52 and 53 to receive the pressure from the oilare made equal on the upper side and the lower side of the spool 40.Therefore, the same effect can be achieved in a case where notches areprovided cross-sectionally symmetrically on the upper and lower sides ofthe axial ends of the stepped down groove 52, which faces the first oilgroove 31, or the stepped down groove 53, which faces the third oilgroove 33, for the purpose of reducing the ripple of the hydraulicpressure.

[0037]FIGS. 6, 7 and 8 show a third embodiment of hydraulic valveaccording to the present invention applied as a directional controlvalve. The directional control valve 60 comprises a valve body 70 and aspool 90, the valve body 70 having an internal spool-receiving room 71whose inner surface is cylindrical, and the spool 90 being inserted andplaced in the spool-receiving room 71. The valve body 70 is alsoprovided with five oil grooves 81, 82, 83, 84 and 85, which are formedperpendicular to the axis of the spool-receiving room 71.

[0038] The first oil groove 81 is located at the central part of thespool-receiving room 71 and connected to P port where pressure oil issupplied from a hydraulic pump (not shown). The second oil groove 82 islocated on the right side of the first oil groove 81 and connected toone of the ports (referred to as “A port”) of a hydraulic actuator, forexample, a hydraulic cylinder (not shown). The third oil groove 83 islocated on the left side of the first oil groove 81 and connected to theother port (referred to as “B port”) of the hydraulic actuator. Thefourth oil groove 84 is located on the left side of the third oil groove83 and connected to T port, which is connected to an oil tank (notshown). The fifth oil groove 85 is located on the right side of thesecond oil groove 82 and connected with the fourth oil groove 84 throughan oil passage L.

[0039] The spool 90 comprises four lands 91, 92, 93 and 94 and threepassages 95, 96 and 97, which are formed successively between the lands91, 92, 93 and 94. The spool 90 is biased rightward by a biasing spring73, which is provided at the left end of the spool-receiving room 71,and leftward by a biasing spring 74, which is provided at the right end.This directional control valve 60 is so designed that the spool 90 willtake a neutral position as shown in FIG. 6 in the equilibrium achievedby these biasing springs 73 and 74 while no pressure oil is suppliedthrough an oil passage 86 into an oil chamber 75 provided at the leftend of the valve body 70 and through an oil passage 87 into an oilchamber 76 provided at the right end of the valve body 70. When thepressure oil is supplied into the oil chamber 75 through the oil passage86 (with the oil chamber 76 at the right end being open to the oiltank), the rightward biasing force generated by the pressure acting onthe spool 90, overcoming the leftward biasing force of the biasingspring 74, shifts and positions the spool 90 at a rightward switchedposition as shown in FIG. 7. On the other hand, when the pressure oil issupplied into the oil chamber 76 through the oil passage 87 (with theoil chamber 75 at the left end being open to the oil tank), the leftwardbiasing force generated by the pressure acting on the spool 90,overcoming the rightward biasing force of the biasing spring 73, shiftsand positions the spool 90 at a leftward switched position as shown inFIG. 8.

[0040] In the directional control valve 60, when the spool 90 ispositioned at the neutral position as shown in FIG. 6, the land 92 shutsthe fluid communication routes between the first oil groove 81 and thethird oil groove 83 and between the third oil groove 83 and the fourthoil groove 84, and the land 93 shuts the fluid communication routesbetween the first oil groove 81 and the second oil groove 82 and betweenthe second oil groove 82 and the fifth oil groove 85. As a result, portsP, T, A and B are all blocked in the valve.

[0041] When the spool 90 is positioned at the rightward switchedposition as shown in FIG. 7, the land 92 shuts the fluid communicationroute between the first oil groove 81 and the third oil groove 83, andthe land 93 shuts the fluid communication route between the second oilgroove 82 and the fifth oil groove 85. However, the third oil groove 83and the fourth oil groove 84 are in fluid communication to each otherthrough the passage 95, and the first oil groove 81 and the second oilgroove 82 are in fluid communication to each other through the passage96. In this condition, ports P and A are in fluid communication to eachother while ports B and T are in fluid communication to each other. As aresult, the hydraulic actuator connected to the directional controlvalve 60 is actuated in a direction which corresponds to the flow of oilthrough these ports.

[0042] On the other hand, when the spool 90 is positioned at theleftward switched position as shown in FIG. 8, the land 92 shuts thefluid communication route between the third oil groove 83 and the fourthoil groove 84, and the land 93 shuts the fluid communication routebetween the first oil groove 81 and the second oil groove 82. However,the first oil groove 81 and the third oil groove 83 are in fluidcommunication through the passage 96, and the second oil groove 82 andthe fifth oil groove 85 are in fluid communication through the passage97. In this condition, ports P and B are in fluid communication to eachother while ports A and T are in fluid communication to each other. As aresult, the hydraulic actuator is actuated in the direction opposite tothe previous direction.

[0043] Furthermore, as shown in FIG. 6, the spool 90 is provided with astepped down groove 931 around the peripheral surface of the land 93,which faces the second oil groove 82 when the spool 90 is positioned atthe neutral position. The stepped down groove 931 is so positioned thatthe axial ends 931 a and 931 b of the stepped down groove 931 having asubstantially constant width axially are, respectively, outside of thesecond oil groove 82 in this condition. The spool 90 is provided alsowith a stepped down groove 921 around the peripheral surface of the land92, which faces the third oil groove 83. This stepped down groove 921 isso positioned that the axial ends 921 a and 921 b of the stepped downgroove 921 having a substantially constant width axially are,respectively, outside of the third oil groove 83 at this neutralposition.

[0044] Moreover, as shown in FIG. 7, another stepped down groove 923 isprovided around the peripheral surface of the land 92, which faces thefirst oil groove 81 when the spool 90 is positioned at the rightwardswitched position. This stepped down groove 923 is so positioned thatthe axial end 923 a of the stepped down groove 923 having asubstantially constant width axially is outside of the first oil groove81 in this condition. Furthermore, another stepped down groove 932 isprovided around the peripheral surface of the land 93, which faces thesecond oil groove 82. This stepped down groove 932 is so positioned thatthe axial end 932 a of the stepped down groove 932 having asubstantially constant width axially is outside of the second oil groove82 in this condition. In addition, another stepped down groove 922 isprovided around the peripheral surface of the land 92, which faces thethird oil groove 83, and this stepped down groove 922 is so positionedthat the axial end 922 a of the stepped down groove 922 having asubstantially constant width axially is outside of the third oil groove83 in this condition. Yet another stepped down groove 911 is providedaround the peripheral surface of the land 91, which faces the fourth oilgroove 84, and this stepped down groove 911 is so positioned that theaxial end 911 a of the stepped down groove 911 having a substantiallyconstant width axially is outside of the fourth oil groove 84 in thiscondition. Still another stepped down groove 933 is provided around theperipheral surface of the land 93, which faces the fifth oil groove 85,and this stepped down groove 933 is so positioned that the axial end 933a of the stepped down groove 933 having a substantially constant widthaxially is outside of the fifth oil groove 85 in this condition.

[0045] As shown in FIG. 8, the spool 90 is provided also with anotherstepped down groove 932 around the peripheral surface of the land 93,which faces the first oil groove 81 when the spool 90 is positioned atthe leftward switched position. This stepped down groove 932 is sopositioned that the axial end 932 a of the stepped down groove 932having a substantially constant width axially is outside of the firstoil groove 81 in this condition. Furthermore, another stepped downgroove 933 is provided around the peripheral surface of the land 93,which faces the second oil groove 82, and this stepped down groove 933is so positioned that the axial end 933 a of the stepped down groove 933having a substantially constant width axially is outside of the secondoil groove 82 in this condition. In addition, another stepped downgroove 923 is provided around the peripheral surface of the land 92,which faces the third oil groove 83, and this stepped down groove 923 isso positioned that the axial end 923 a of the stepped down groove 923having a substantially constant width axially is outside of the thirdoil groove 83 in this condition. Yet another stepped down groove 922 isprovided around the peripheral surface of the land 92, which faces thefourth oil groove 84, and this stepped down groove 922 is so positionedthat the axial end 922 a of the stepped down groove 922 having asubstantially constant width axially is outside of the fourth oil groove84 in this condition. Still another stepped down groove 941 is providedaround the peripheral surface of the land 94, which faces the fifth oilgroove 85, and this stepped down groove 941 is so positioned that theaxial end 941 a of the stepped down groove 941 having a substantiallyconstant width axially is outside of the fifth oil groove 85 in thiscondition.

[0046] Also, the valve body 70 of the directional control valve 60 is anarticle of cast metal produced by die casting, so each of the abovementioned oil grooves 81, 82, 83, 84 and 85 has a draft or slight taper,which is used for facilitating the removal of the die assembly duringthe production of the valve body. Because of the existence of a draft,the length of each oil groove in the axial direction of the spool 90 issmaller for the part of the oil groove located deeper in the valve body(part located lower in the drawing) and larger for the part locatedshallower. In the directional control valve 60, the spool 90, which ispositioned at the switched positions (including the neutral position),is provided with the stepped down grooves 911, 921, 922, 923, 931, 932,933 and 941 that extend around the peripheral surfaces of the lands 91,92, 93 and 94, respectively, which face the oil grooves 81, 82, 83, 84and 85 as described above. Therefore, the oil in the oil grooves flowsinto the corresponding stepped down grooves and surrounds and pushes theperipheral surfaces in the direction perpendicular to the axis of thespool 90 (in the upward and downward directions in the drawing). Becausethe axial ends of the stepped down grooves are located axially outsideof the corresponding oil grooves at the switched positions, the pushingforce acting on the peripheral surface of each stepped down groove isdistributed evenly all around the peripheral surface. Therefore, nounbalanced force is generated around the peripheral surface, so themovement of the spool 90 is smoother than that of a prior-artcounterpart. In addition, the valve body 70 is less prone to erosionthan a prior-art counterpart because no or little unbalanced load actsto push the spool 90 onto the valve body 70.

[0047] In the above described directional control valve 60, a hydraulicpilot control is used to shift the spool 90 axially. Instead, anelectromagnetic drive may be applied, or the spool 90 may be shiftedmanually or mechanically. Also, instead of the hydraulic pilot control,the driving method used for shifting the spool 40 in the previouslydescribed regulator valve 10 may be also applied for shifting the spool90 in the directional control valve 60. In this case, part of the firstembodiment is applicable to the directional control valve.

[0048] In the above description, each of the stepped down grooves 911,921, 922, 923, 931, 932, 933 and 941 is described to have asubstantially constant width in the axial direction. However, it is notnecessary for each stepped down groove to have a constant width allaround the spool 90. As in the case of the regulator valve 10 describedpreviously, the same beneficial effect can be achieved by forming thestepped down grooves in an up-and-down symmetry in the cross-section ofthe spool 90. Therefore, the same effect can be achieved in a case wherenotches are provided cross-sectionally symmetrically on the upper andlower sides of the axial ends of the stepped down grooves 911, 921, 922,923, 931, 932, 933 and 941.

[0049] Preferred embodiments of hydraulic valve according to the presentinvention are described above. However, the scope of the presentinvention is not limited to those embodiments. In the above description,the first and second embodiments of hydraulic valve according to thepresent invention are applied to a regulator valve. These are onlyexamples. The same embodiments may be applied to a reducing valve, to adirectional control valve or to a flow-control valve.

[0050] In the above embodiments, stepped down grooves are providedaround the peripheral surfaces of the spool to eliminate unfavorableeffects of drafts remaining on the inner surfaces of the oil grooves,which are formed by molding. However, unbalanced loads may occur fromreasons other than oil grooves with slight tapers. For example, oilgrooves whose inner surfaces are not finished to an adequate precisioncan cause unbalanced loads to act on the spool. In such a case, steppeddown grooves are also applied to eliminated the problem.

[0051] As described above, in the first embodiment of hydraulic valveaccording to the present invention, a stepped down groove is providedaround the peripheral surface of the spool, so that the stepped downgroove faces the oil groove. In this arrangement, oil in the oil grooveflows into the stepped down groove and pushes the peripheral surface inthe direction perpendicular to the axis of the spool. Because the axialends of the stepped down groove are located axially outside of the axialends of the oil groove at least while the hydraulic valve is inpressure-adjusting condition, the pushing force acting on the peripheralsurface of the stepped down groove is distributed evenly all around theperipheral surface. Therefore, no unbalanced force is generated aroundthe peripheral surface, so the movement of the spool is smoother thanthat of a prior-art counterpart. In addition, the valve body is lessprone to erosion than a prior-art counterpart because no or littleunbalanced load acts to push the spool onto the valve body.

[0052] In the second embodiment of hydraulic valve, a stepped downgroove is provided around the peripheral surface of the spool, so thatthe stepped down groove faces the oil groove. In this arrangement, oilin the oil groove flows into the stepped down groove and pushes theperipheral surface in the direction perpendicular to the axis of thespool. Because the axial ends of the stepped down groove come axially tothe right and left sides, respectively, of the axial end of the oilgroove to which end the spool shifts to increase the opening of the oilgroove at least while the valve is in pressure-adjusting condition, thepushing force acting on the peripheral surface of the stepped downgroove is distributed evenly all around the peripheral surface.Therefore, no unbalanced force is generated around the peripheralsurface, so the, movement of the spool is smoother than that of aprior-art counterpart. In addition, the valve body is less prone toerosion than a prior-art counterpart because no or little unbalancedload acts to push the spool onto the valve body.

[0053] In the third embodiment of hydraulic valve according to thepresent invention, a stepped down groove is provided around theperipheral surface of a land of the spool, so that the stepped downgroove faces the oil groove when the spool is positioned at eachswitched position. In this arrangement, oil in the oil groove flows intothe stepped down groove and pushes the peripheral surface in thedirection perpendicular to the axis of the spool. Because the axial endof the stepped down groove comes axially outside of the oil groove whenthe spool is at any switched position, the pushing force acting on theperipheral surface of the stepped down groove is distributed evenly allaround the peripheral surface. Therefore, no unbalanced force isgenerated around the peripheral surface, so the movement of the spool issmoother than that of a prior-art counterpart. In addition, the valvebody is less prone to erosion than a prior-art counterpart because no orlittle unbalanced load acts to push the spool onto the valve body.

[0054] The invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

RELATED APPLICATIONS

[0055] This application claims the priority of Japanese PatentApplication No.2001-345254 filed on Nov. 9, 2001, which is incorporatedherein by reference.

What is claimed is:
 1. A hydraulic valve comprising: a valve body whichhas an internally cylindrical spool-receiving room and an oil grooveprovided orthogonally to an axis of said spool-receiving room, and aspool, which is inserted in said spool-receiving room; wherein: astepped down groove is provided around a peripheral surface of saidspool, so that a hydraulic pressure supplied into said oil groove ismade to act on said spool at said stepped down groove so as to eliminatepossibility of an unbalanced load acting on said spool in a directionperpendicular to an axis of said spool.
 2. The hydraulic valve as setforth in claim 11 wherein: said stepped down groove is formed in acylindrical tube figure, coaxially to said spool; and lateral faces ofsaid stepped down groove are orthogonal to the axis of said spool. 3.The hydraulic valve as set forth in claim 1, wherein: said spool isshifted axially in correspondence to an actuation pressure beingsupplied into said oil groove; said stepped down groove is provided onthe peripheral surface of said spool that faces said oil groove; andboth axial ends of said stepped down groove are located axially outsideof both axial ends of said oil groove at least while said hydraulicvalve is in pressure-adjusting condition.
 4. The hydraulic valve as setforth in claim 1, wherein: said spool is axially shifted to change axiallength of part of a land that is axially in said oil groove so as toadjust opening of said oil groove; said stepped down groove is providedon a peripheral surface of said land; and both axial ends of saidstepped down groove come axially right and left sides, respectively, ofthe axial end of said oil groove located on a side to which said spoolshifts to increase said opening, at least while said hydraulic valve isin pressure-adjusting condition.
 5. The hydraulic valve as set forth inclaim 1, wherein: said spool is axially shifted to switch positions, sothat said oil groove is communicated and blocked in correspondence tothe switched positions; said stepped down groove is provided on aperipheral surface of a land of said spool that faces said oil groovewhen said spool is positioned at each switched position; and an axialend of said stepped down groove is axially outside of said oil groovenotwithstanding the switched position of said spool.